Usually one or more reverse gears are realized with a so-called reverse gear intermediate wheel for reversal of rotation in connection with discrete ratio transmissions for motor vehicles with coaxial drive and output shaft, as this is described in the framework of DE 199 54 130 A1 of the Applicant. This intermediate gear for the reverse gear is freely pivoted on a defined position in the transmission housing and, as a rule, meshes with a running gear on the countershaft or driving shaft and a running gear on the main shaft or driven shaft.
Alternatively, the intermediate gear for the reverse gear can also engage into a gearing of the drive shaft and a gearing of the countershaft as driven shaft.
All transmissions known today have a position for the intermediate gear for the reverse gear which is supposed to keep the bearing reaction forces on the transmission housing as low as possible in reverse gear traction operation and which, as a rule, has the greater bearing forces on the housing in reverse gear pushing operation (with low running times).
This position for the intermediate gear for the reverse gear is defined as follows according to the state of the art.
If one extends an imaginary plane that passes through the axes of rotation of the driving and the output shafts and orients this plane horizontally so that the driving shaft is located to the right of the output shaft in the direction of travel, then the preferred position for the intermediate gear for the reverse gear is always situated beneath this plane.
In certain motor vehicle segments, according to the prior art, the drive of power take-offs takes place through an additional intermediate shaft, which engages into the intermediate gear for the reverse gear. An example of a transmission constructed in this manner is the transmission model ECOMID by the Applicant, as it is known from Looman, Gear Transmissions, 3rd Edition, Springer Publishing Company, page 263.
A disadvantage of the position described for the intermediate gear for the reverse gear is that, this way, very large bearing reaction forces upon the transmission housing result if the power take-off is being driven. These high bearing reaction forces restrict the maximally allowable torque and the life expectancy for the power take-off operation. A functional disadvantage in relation to transmissions in which the power take-off is driven directly coaxially by the countershaft, as is the case in the models ECOSPLIT and ASTRONIC of the Applicant. In this context, it should be pointed out that the required life for the power take-off operation is many times higher than the life required for the reverse gear operation.
The direct drive of the power take-off, co-axially via the countershaft, is nonetheless only possible in many cases, for example with range-change transmissions with a rear-mounted range-change unit in planetary construction, if the center distance between main shaft and countershaft is sufficiently large. A sufficiently large center distance, in turn, results in correspondingly large and difficult-to-build transmissions with correspondingly high production costs.
The present invention is based upon the object of providing an arrangement of the intermediate gear for the reverse gear in connection with a discrete ratio transmission with co-axial drive and output shafts and at least one additional intermediate shaft for a power take-off that optimizes the life of the power take-off. In particular, large bearing reaction forces on the transmission housing, when the power take-off is being driven, are to be avoided.
Moreover, the maximally allowable torque in the power take-off operation is to be increased.